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apparmor: add signal and ptrace rules for stacked profiles #919

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apparmor: add signal and ptrace rules for stacked profiles #919

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4 changes: 4 additions & 0 deletions common/pkg/apparmor/apparmor_linux_template.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@ profile {{.Name}} flags=(attach_disconnected,mediate_deleted) {
# Allow signals from privileged profiles and from within the same profile
signal (receive) peer=unconfined,
signal (send,receive) peer={{.Name}},
# With AppArmor 5.0+, child processes get a stacked profile.
signal (send,receive) peer={{.Name}}//&*,

@Luap99 Luap99 Jun 16, 2026

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can you link to official docs for this syntax/change?

Also is this fully backwards compatible? What happens if the rule is loaded on apparmor 4 or earlier will the parser accept that?

@bitoku bitoku Jun 17, 2026 •
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https://gitlab.com/apparmor/apparmor/-/wikis/Release_Notes_5.0.0

I can't find the release note about this change, but apparently AI found the change that caused the issue (sorry about just putting the AI result, but I believe it'll help).

According to the AI , torvalds/linux@a9eb185 this change caused the issue. The AI summary is below.

Details

What changed

Previously, x_to_label() in security/apparmor/domain.c only checked whether the first entry in the exec transition table started with & (the stacking marker).
If the first entry wasn't a stack, stacking was skipped entirely — even if a later entry that actually matched did start with &.

The fix checks the actually matched entry for the & prefix:

  // Before: checked first entry only
  stack = rules->file->trans.table[xindex & AA_X_INDEX_MASK];
  if (*stack != '&') { /* skip stacking */ }
  // After: checks the matched entry
  new = x_table_lookup(profile, xindex, lookupname);
  if (!new || **lookupname != '&')
      break;
  stack = new;

Why this breaks container profiles

With the fix, exec'd processes inside containers now correctly receive a stacked label like cri-containerd.apparmor.d//&unconfined (or crio-default//&crun),
where previously the stacking was silently skipped and they just got cri-containerd.apparmor.d.

Existing signal/ptrace rules like signal (send,receive) peer={{.Name}} only match the bare profile name, not the stacked compound label — hence the DENIED
audit entries.

This has also the detailed explanation, but not mention about the upstream change.
containerd/containerd#12886

I confirmed the config is valid in apparmor 4 environment, but I just ran the reproducer, so not sure if it covers enough scenarios.

# Allow certain signals from OCI runtimes (podman, runc and crun)
signal (receive) peer={/usr/bin/,/usr/sbin/,}runc,
signal (receive) peer={/usr/bin/,/usr/sbin/,}crun*,
Expand Down Expand Up @@ -48,6 +50,8 @@ profile {{.Name}} flags=(attach_disconnected,mediate_deleted) {
{{if ge .Version 208095}}
# suppress ptrace denials when using 'ps' inside a container
ptrace (trace,read) peer={{.Name}},
# With AppArmor 5.0+, child processes get a stacked profile.
ptrace (trace,read) peer={{.Name}}//&*,
{{end}}
}
`
29 changes: 29 additions & 0 deletions common/pkg/apparmor/apparmor_linux_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,11 @@
package apparmor

import (
"bytes"
"os"
"strings"
"testing"
"text/template"
)

type versionExpected struct {
Expand Down Expand Up @@ -130,6 +133,32 @@ func TestInstallDefault(t *testing.T) {
checkLoaded(false)
}

func TestStackedProfileRules(t *testing.T) {
compiled, err := template.New("apparmor_profile").Parse(defaultProfileTemplate)
if err != nil {
t.Fatalf("Failed to parse template: %v", err)
}

p := profileData{
Name: "test-profile",
Version: 300000,
}

var buf bytes.Buffer
if err := compiled.Execute(&buf, p); err != nil {
t.Fatalf("Failed to execute template: %v", err)
}

output := buf.String()

if !strings.Contains(output, "signal (send,receive) peer=test-profile//&*,") {
t.Error("Missing stacked profile signal rule")
}
if !strings.Contains(output, "ptrace (trace,read) peer=test-profile//&*,") {
t.Error("Missing stacked profile ptrace rule")
}
}

func TestDefaultContent(t *testing.T) {
if _, err := os.Stat(aapath); err != nil {
t.Skip("AppArmor isn't available in this environment")
Expand Down
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